The aim of this proposal is to learn the exact relationships between ultrasound energy absorption in the explanted rat embryo and subsequent in vitro growth of the exposed embryo. A dosimetric approach to the exposure conditions will be employed. The upper exposure condition will yield hyperthermic temperatures and the lower exposure will be less than the American Institute of Ultrasound Medicine Bioeffect Statement, that is, less than 50J/cm2 in the 1 to 500 second exposure time region. By in situ temperature measurements of the embryo during ultrasound exposure, exact exposure conditions will allow us to determine the appropriate dose range for our experiments. The culture system is a well established method which allows measurement of normal growth and development of the isolated embryo for a period of 1 to 2 days during embryogenesis. After establishing a range of doses (time and intensity), we will study their effect during a subsequent 24 hour growth period. Sham treated embryos from the same litters will serve as controls. The end-points to be measured in these embryos are crown-rump length, somite count, morphologic markers, total protein and DNA content. Histologic sections will be made of selected embroyos. We hope by the application of these rigorous exposure conditions to this embryo culture to establish basic information for use in establishing risk assessment.